Cannabinoids, the primary bioactive constituents of marijuana, are being extensively studied in order to understand their toxic and immunotherapeutic potential. They activate CB1 and CB2 receptors and signal through an endogenous cannabinoid system. Expression of the CB2 receptor predominates in cells from the immune system, and our novel preliminary findings suggest that CB2 is not only an extracellular G-protein- coupled receptor but is expressed at different locations and in different amounts by immune cells. While human B cells express CB2 on the cell surface, they also express a high intracellular concentration of CB2. In contrast, T cells do not express extracellular CB2 but express intracellular protein. In addition, CB2 expression patterns change in malignant B cell lines and change when nave B cells are activated. These novel findings lead us to hypothesize that CB2 receptor expression, location, and trafficking are critical features tha link cannabinoids to specific signaling and functional consequences. Three specific aims are proposed: Aim 1) To investigate the role of CB2 receptor internalization and the use of adaptor proteins on the cellular distribution of CB2 in immune cells. Experiments will define CB2 location within the cell and assess if location differs by cell type, if intracellular CB2 is accessible to ligand binding, if cannabinoids differ in their ability to access intracellular CB2, and the role tat receptor internalization, recycling and adaptor proteins play in controlling CB2 distribution. Aim 2) To investigate the two-way interaction between CB2 expression on B cells, the impact of B cell activation on CB2 expression, and the capacity for cannabinoids to regulate B cell differentiation and immunoglobulin (Ig) class switching. We hypothesize that CB2 expression is a regulated event, and its expression pattern will bias responder cells toward specific differentiation pathways. Aim 3) To link signaling to location and the functional role of CB2 receptors. Cells with different CB2 expression patterns and cells in which the expression patterns have been specifically manipulated / activated will be assessed for cannabinoid signaling via three pathways - ERK/MAPK, PI3K/AKT, and intracellular Ca++. By the conclusion of these studies, we hope to better understand how CB2 receptor location, internalization, and trafficking link to the biologic effects of cannabinoids on human immune cells.